The Superior Fascicle of the Anterior Talofibular Ligament Functions as a Restraint Against Internal Rotation: A Cadaveric Biomechanical Study

BACKGROUND: Lateral ankle sprains frequently result in anterior talofibular ligament (ATFL) dysfunction, leading to chronic lateral ankle instability. The ATFL consists of superior and inferior fascicles; however, the stabilizing role of the superior fascicle remains unclear. We biomechanically evaluated its function using cadaveric models. METHODS: Nine frozen cadaveric ankles were tested using a robotic system (FRS2015). The superior fascicle was sequentially transected arthroscopically to simulate cumulative 3 injury types: type 1, partial detachment at the medial margin of the fibular attachment; type 2, proximal detachment; and type 3, complete detachment. Anterior talar translation, internal rotation, and inversion angles relative to the tibia were measured as displacements under the anterior drawer, internal rotation, and inversion loads, respectively, at 15° dorsiflexion and 15° and 30° plantarflexion. In situ forces and ankle kinematics were also measured. RESULTS: = .02). With the numbers available, no significant differences were found among intact, type 1, and type 2, nor in anterior or inversion displacement across any conditions. The in situ force was greater in type 3 than in type 1 during anterior drawer and internal rotation loading, and ankle kinematics did not differ. CONCLUSION: Partial injury to the superior fascicle of the ATFL was not associated with a statistically significant difference in ankle instability under the tested conditions, whereas complete injury was associated with significantly greater internal rotational displacement. CLINICAL RELEVANCE: Injury to the superior fascicle of the ATFL is associated with increased internal rotational laxity, supporting the use of internal rotation testing, such as the anterolateral drawer test, when evaluating suspected ATFL injury.